Final answer:
As Carnegie Steel became more profitable, Andrew Carnegie bought out his business partner in order to further expand and consolidate his control over the steel industry.
Step-by-step explanation:
As Carnegie Steel became more profitable approaching 1890, Andrew Carnegie chose to buy out his business partner in order to further expand and consolidate his control over the steel industry. Carnegie was known for his shrewd business decisions and his ability to locate financial backing for his enterprise. He saved his profits during prosperous times and used them to buy out other steel companies at low prices during economic recessions. By buying out his partner, Carnegie was able to maintain complete control over his steel empire and continue his dominance in the industry.